The present invention relates to opacity testing apparatus and in particular to apparatus for sampling the exhaust of internal combustion (i.e., diesel or gas) engines and determining the relative opacity or particulate content of the exhaust.
As exhaust emission standards are implemented by the Federal and State Governments, it becomes necessary for the truck and auto manufacturers and, in particular the engine designers to design engines that meet the emission standards. One of such standards is directed to the particulate emissions from such engines and the measure of which emissions is related to an optical percentage scale and against which the clarity or opacity of the emissions are measured. Because such standards are only of recent origin, most test equipment is only presently undergoing development, although some equipment does exist relative to monitoring smoke stacks or the like. This inventor is also aware of a previously developed system that is sold by Celesco/Berkeley and which is manufactured by Telonic Berkeley of Irvine, California for measuring engine exhaust, but which system has an optical sampling head that attaches to the exhaust pipe and whereat the opacity of the exhaust is directly and optically monitored across the exhaust outlet. Shortfalls of this equipment, however, are that it has a rather cumbersome optical sampling head which can become optically misaligned during handling in addition to which it produces large amounts of noise. This noise is superimposed on the electrically measured output signal, thus limiting the sensitivity of the equipment and producing a relatively unstable zero reference signal level.
Because of these various shortcomings and due to a desire to develop test equipment that is more compatible with efficient testing procedures, the present rack-mounted assembly was developed. This equipment essentially comprises a sampler tube for coupling a portion of the engine exhaust to a valve, whereat clean air may be alternatively admitted, such as at the end of a test run and prior to admitting the exhaust air to a closed-loop opacity chamber. The present opacity chamber, in turn, is comprised of a differentially pressurized, bifurcated path whereby the sample is divided at an input port and caused to flow into oposite ends of the sample tube and exit from an outlet port that is coupled midway therealong to an appropriate air pump. The flow is thus directed from opposite ends of the opacity chamber, towards the center, while an appropriately shaped and amplified pulsed beam of light is directed from one end and through the center of the chamber to the other end and whereat the emerging light is compared to a reference light level that is determined from the pulsed light source so as to generate a related percentage of opacity. Alternative reference light sources are further disclosed, wherein in one embodiment, a beam splitter is employed in conjunction with a reference detector; and wherein in a second embodiment, the reference detector and opacity detector are mounted in the same ambient environment, while the reference detector responsively detects the back light of the pulsed light source. The details thereof will, however, become more apparent upon reference to the following description of the present invention with respect to the following drawings.
Before referring thereto, however, it is to be recognized that the present invention is described with respect to its presently preferred embodiment and, therefore, that various modifications may be made thereto without departing from the spirit and scope of the described invention. Accordingly, the present invention is not to be limited only to that configuration disclosed hereinafter.